Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/30—Electroplating: Baths therefor from solutions of tin
  • C25D3/32—Electroplating: Baths therefor from solutions of tin characterised by the organic bath constituents used
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions

Definitions

• Electroplating solutions are usually aqueous. Every plating solution contains ingredients to perform at least the first, and usually several, of the following functions: (1) provide a source of ions of the metal(s) to be deposited; (2) form complexes with ions of the depositing metal; (3) provide conductivity; (4) stabilize the solution against hydrolysis or other forms of decomposition; (5) buffer the pH of the solution; (6) regulate the physical form of the deposit; (7) aid in anode corrosion; and (8) modify other properties peculiar to the solution involved.
• the present invention improves the plating performance of the solution, particularly by increasing the useful current density over previously accepted norms.
• the current density is the average current in amperes divided by the area through which that current passes; the area is usually nominal area, since the true area for any but extremely smooth electrodes is seldom known. Units used in this regard are amperes per square meter (A/m 2 ).
• a variety of metals and metal alloys are commercially plated from solutions with sulfate as the primary anion. See for example U.S. Patent Nos. 4,347, 107; 4,331,518 and 3,616,306.
• Certain sulfate electroplating baths have limitations that can sometimes be alleviated with the addition of additives including other anions.
• the steel industry has been tin plating steel for many years from sulfuric acid/ tin sulfate baths where phenol sulfonic acid is used as a special electrolyte additive which improves both the oxidative stability of the tin as well as increasing its current density range. This is known as the ferrostan process but because of environmental problems with phenol derivatives the steel industry is looking to replace this bath with one which is less harmful to the environment.
• nickel sulfate is used for nickel plating but nickel chloride must also be present to provide enough conductivity and improve anode dissolution.
• This bath is known as the Watts bath but although economical, suffers from a number of disadvantages including a nickel plate that is highly stressed.
• alkyl sulfonic acid baths include low corrosivity, high solubility of salts, good conductivity, good oxidative stability of tin salts and complete biodegradability.
• the predominant metals plated in these sulfonic acid baths are tin, lead and copper as well as alloys of these metals with each other.
• Fiuoroborate plating baths are widely used for coating a variety of metals on all types of metal substitutes including both copper and iron. See for example, U.S. Patent Nos. 5,431,805; 4,029,556 and 3,770,599. These baths are preferred where plating speed is important and the fiuoroborate salts are very soluble.
• a variety of additives have been developed to improve the performance of these baths. These additives either improve the quality of the deposit, the efficiency of the bath or they reduce environmental effects. See for example, U.S. Patent No. 4,923,576.
• 5,628,893 and 5,538,617 describe additives which can be used in a halogen tin plating bath for the purpose of reducing sludge formation by stabilizing the tin against oxidation.
• additives for the tin bath described in U.S. Patent Nos. 5,628,893 and 5,538,617 improve the efficiency of the bath and by decreasing the amount of waste also reduce the environmental effects.
• One embodiment of the present invention relates to the use of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts of alkyl and alkanol sulfonic acid which have been found to improve the performance of sulfate electroplating baths.
• these salt additives were found to generally increase the plating range so that these baths can be used at much higher current densities. Thus these baths can be run at greater speeds than those without these additives. Further improvements are seen in the quality of the deposits. In the case of stannous sulfate plating solutions, some improvements in the oxidative stability of the tin was also observed.
• one preferred embodiment of the present invention is directed to a method of improving the plating performance of an aqueous sulfate based electroplating bath comprising the step of adding an effective performance enhancing amount of a salt of an alkyl and/ or alkanol sulfonic acid to said bath.
• the salts used to improve the bath plating performance characteristics are particularly selected from the group consisting of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts.
• alkali metal alkaline earth metal
• ammonium alkali metal
• substituted ammonium salts especially preferred are salts of 2-hydroxy ethyl sulfonic acid, especially the sodium salt (sodium isethionate).
• the baths that can be improved by this embodiment include tin and tin alloys, nickel and nickel alloys, copper and copper alloys, chromium and chromium alloys, cadmium and cadmium alloys, iron and iron alloys, rhodium and rhodium alloys, ruthenium and ruthenium alloys, and especially the iron/ zinc and tin/ zinc alloy plating baths.
• tin and tin alloy baths are improved by this embodiment of the invention.
• examples include tin-antimony, tin-cadmium, tin-copper, tin- lead, tin-nickel, tin-niobium, tin-titanium, tin-zirconium, and tin -antimony- copper alloy baths. Alloy compositions comprising these metals are well known to those having ordinary skill in this art, and are the subjects of numerous patents.
• Another preferred embodiment of the present invention relates to the use of salts of alkyl and alkanol sulfonic acid which were found to improve the performance of sulfonic acid, especially alkyl sulfonic acid electroplating baths.
• the salts are selected from the group consisting of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts of 2-hydroxy ethyl sulfonic acid (isethionic acid).
• these salts are not harmful to the environment, they are completely biodegradable and the products of the biodegradation are common ions and molecules found in the environment. In addition they have a number of other advantages including high solderability, low corrosivity to equipment, good stability at high temperatures, and compatibility with many other metal salts.
• these baths will also contain the corresponding metal salt or metal salts if an alloy plate is required, and various additives to control the quality and appearance of the plated surface and the stability of the bath solution.
• Typical additives include a surfactant such as an ethoxylated fatty alcohol, a brightening agent if required and an antioxidant such as hydroquinone or catechol, if tin is one of the metals being plated.
• Another advantage of using the salts of alkyl or alkanol sulfonates is that they are much less expensive than their corresponding acid.
• the only bulk commercial alkyl/ alkanol sulfonic acid suitable for electroplating is methane sulfonic acid and the only bulk commercial alkali/ alkaline earth/ ammonium alkyl/ alkanol sulfonate salt suitable for electroplating is sodium isethionate.
• the sodium isethionate is less than half the price of the methane sulfonic acid either on a mole basis or on a weight basis.
• Another embodiment of the present invention relates to the use of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts of alkyl and alkanol sulfonic acid which were found to improve the performance of fiuoroborate electroplating baths.
• these salt additives were found to generally increase the plating range so that these baths can be used at much higher current densities, thus these baths can be run at greater speeds than those without these additives. Further improvements are seen in the quality of the deposits.
• this embodiment of the present invention is directed to a method of improving the plating performance of a fiuoroborate ion based electroplating bath comprising the step of adding an effective performance enhancing amount of a salt of an alkyl and/ or alkanol sulfonic acid to said bath.
• the salts used to improve the bath plating performance characteristics are particularly selected from the group consisting of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts.
• alkali metal alkaline earth metal
• ammonium alkali metal
• substituted ammonium salts especially preferred are salts of 2-hydroxy ethyl sulfonic acid, especially the sodium salt (sodium isethionate).
• the baths that can be improved by this embodiment include tin and tin alloy plating baths; nickel and nickel alloy plating baths; copper and copper alloy plating baths; zinc or zinc alloy plating baths; as well as cadmium and cadmium alloy plating baths.
• Yet another embodiment of the present invention relates to the use of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts of alkyl and alkanol sulfonic acid which have been found to improve the performance of halide electroplating baths.
• these salt additives were found to generally increase the plating range so that these baths can be used at much higher current densities than previously. Thus these baths can be run at greater speeds than those without these additives. Further improvements are seen in the quality of the deposits.
• this embodiment of the present invention is directed to a method of improving the plating performance of an aqueous halide ion based electroplating bath comprising the step of adding an effective performance enhancing amount of a salt of an alkyl and/ or alkanol sulfonic acid to said bath.
• the halide ion of the bath is usually either chloride or fluoride.
• the salts used to improve the bath plating performance characteristics are particularly selected from the group consisting of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts. Especially preferred are salts of 2-hydroxy ethyl sulfonic acid, especially the sodium salt (sodium isethionate).
• the baths that can be improved by this embodiment include tin and tin alloy plating baths; nickel and nickel alloy plating baths; copper and copper alloy plating baths; zinc or zinc alloy plating baths; as well as cadmium and cadmium alloy plating baths.
• alkali metal, alkaline earth metal, ammonium and substituted ammonium salts of alkyl and alkanol sulfonic acids as additives in pure metal and metal alloy sulfate electroplating baths has a number of unexpected benefits including wider useful current density range, improved appearance and in the case of tin improved oxidative stability. These baths can be run at greater speeds than those without these additives. Further improvements are seen in the quality of the deposits and greater tolerance to impurities such as iron. In the case of stannous sulfate plating solutions some improvements in the oxidative stability of the tin was also observed. [0034] Unlike phenol sulfonic acid these salts are not harmful to the environment.
• These baths also contain the corresponding metal salt or metal salts if any alloy plate is required, and various additives to control the quality and appearance of the plated surface and the stability of the bath solution.
• Typical additives include a surfactant such as an ethoxylated fatty alcohol, a brightening agent if required and an antioxidant such as hydroquinone or catechol, if tin is one of the metals being plated.
• Plating tests have proven than additions of sodium isethionate to a known MSA Tin/ Lead system allow the decrease of the amount of methane sulfonic acid required in the plating bath.
• the decrease in MSA, with the addition of sodium isethionate allows for optimum bath performance with a decrease in cost and an overall lightening of the tin or tin/ lead deposit.
• Plating tests were performed with a decrease of the acid to 1 / 3 typical level and no negative effects were noted. Some plating tests showed a significant improvement of the overall deposit with additions of sodium isethionate.
• a decrease in the burn and band(s) opened up the upper CD range.
• a commercially available plating system (Technic MSA 90/ 10, Technic, Inc.) had an increase in CD range from 120 ASF to greater than 240 ASF.
• a typical commercial MSA plating system contains approximately
• Plate Conditions 10 A, 1 min, 1500 rpm, 110°F. An increase in amperage was attempted for this plating system under these plate conditions.
• Example 4 shows the results of the plating bath listed above with no sodium isethionate additions.
• Example 5 shows the results of the plating bath listed above, under the same plating conditions with a 15 g/1 sodium isethionate addition.
• Plate Conditions 10 a, 1 min, 1500 rpm, 110°F. An increase in amperage was attempted for this plating system under these plate conditions.
• Example 6 shows the results of the plating bath listed above, with no sodium isethionate additions.
• Example 7 shows the results of the plating bath listed above, under the same plating conditions with a 15 g/1 sodium isethionate addition.
• the CD ranges of both 10 amp panels look similar. However, the initial panel without the presence of sodium isethionate, has treeing along the panel edge. There is no treeing visible on the panel with the sodium isethionate addition. In application, the presence of the treeing would actually narrow the operating range of the plating bath.
• both sodium methane sulfonate and sodium isethionate additions look to have similar benefits.
• the additions of sodium isethionate are preferred however, since the sodium isethionate minimizes the burn as compared to the sodium methane sulfonate. In practice there would be a wider operating window.
• the sodium isethionate lightens the overall deposit evenly across the entire CD range.
• This example illustrates the ability of the alkanol sulfonate salt to inhibit the oxidation of the stannous ion in methane sulfonate based tin plating bath solutions.
• alkali metal, alkaline earth metal, ammonium and substituted ammonium salts of alkyl and alkanol sulfonic acids as additives in pure metal and metal alloy fiuoroborate electroplating baths has a number of unexpected benefits including wider useful current density range and improved appearance.
• the metals and metal alloys include but are not limited to tin, lead, copper, cadmium, indium, iron, tin/lead and tin/lead copper.
• This Example shows that upon addition of sodium methane sulfonate or sodium isethionate, this bath can be used at a higher current density and the appearance of the coating expands.
• alkali metal, alkaline earth metal, ammonium and substituted ammonium salts of alkyl and alkanol sulfonic acids as additives in pure metal and metal alloy halide electroplating baths has a number of unexpected benefits including wider useful current density range and improved appearance.
• the metals and metal alloys include, but are not limited to tin, lead, copper, nickel, zinc, cadmium, tin/zinc, zinc/nickel and tin/nickel.
• Plating strips were made of steel and were pretreated by soaking for 15 seconds in an alkali, rinsing then immersing for 15 seconds in 10% sulfuric acid and rinsing again.
• the mixture of different ionic species forms a unique combination that can produce metallic coatings with required properties. It is well known that the overall ionic conductivity of the solution depends on the character of individual ionic species and their concentrations. The specific interactions between different ionic species and/or solvent molecules determine the overall conductivity and may affect electrodeposition processes. However, ionic conductivity is only one variable, which must be considered in formulating plating baths.
• T M activity coefficient of the species Met n+ in the bulk solution ⁇ a apparent transfer coefficient for reduction n number of electrons involved in electroreduction
• the cation and/ or anion are not added only to preserve ionic conductivity of the electrolyte and/ or solubility of deposited ion(s); instead they directly affect the electrodeposition process, by affecting the double layer structure and in consequence the mechanism of the electroreduction process.
• a method of improving the plating performance of an aqueous electroplating bath selected from the group consisting of sulfate, sulfonic acid, fiuoroborate, and halide electroplating baths comprising the step of adding an effective performance enhancing amount of a salt of an alkyl and/ or alkanol sulfonic acid to said bath.
• salts are selected from the group consisting of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts.

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• 2000
  • 2000-03-17 WO PCT/US2000/007362 patent/WO2000056952A1/en active IP Right Grant
  • 2000-03-17 JP JP2000606810A patent/JP2002540291A/ja active Pending
  • 2000-03-17 AU AU36321/00A patent/AU773971B2/en not_active Ceased
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